1. Technical Field
Embodiments of this disclosure relate to an image forming apparatus, such as a copier, a printer, a facsimile machine, or a printing press.
2. Description of the Related Art
Image forming apparatuses are used as, for example, copiers, printers, facsimile machines, printing presses, and multi-functional devices having at least one of the foregoing capabilities. As one type of image forming apparatus, an image forming apparatus is known that performs correction and control to reduce uneven density of a toner image formed on an image carrier.
For example, JP-S62-145266-A proposes a technique of recording a black solid image on a photoreceptor drum, reading the black solid image to store data of the black solid image, and correcting image density at each recording position, based on the read information prior to image output, in a recording apparatus (image forming apparatus) that modulates a laser beam on the photoreceptor drum (image carrier), scans the result to thereby record a latent image, and develops/transfers the latent image by an electrophotographic process to output the same. Moreover, in JP-H09-062042-A, there is disclosed an image forming apparatus in which an image formation condition of at least one of a charging voltage, an exposure light volume, a development voltage and a transfer voltage is controlled, based on periodic variation data of image density stored in advance or periodic variation data of a charging potential of an image carrier, by which striped uneven density, which occurs periodically in an image, is reduced. Moreover, in JP-3825184-B, there is disclosed an image forming apparatus that senses a rotation period of a development roller in a development-roller rotation period sensing device, senses an amount of uneven density of a toner of a pattern formed on an image carrier in an uneven-density-amount sensing device, and controls a development bias so as to match an output signal of the uneven-density-amount sensing device and an output signal of the development-roller rotation period sensing device in phase. In this image forming apparatus, changing a development potential by the control of the development bias enables the uneven density of a solid image to be corrected. Moreover, in JP-2006-106556-A, there is disclosed an image forming apparatus that causes a test image to be formed on an image carrier or on a transfer medium to detect a frequency of periodic uneven image density occurring in the test image and to specify a source of the uneven image density, based on the detected frequency, and controls operation of the specified source of the uneven image density so as to reduce the uneven image density.
When the image forming condition such as the development bias is periodically changed to cancel the uneven density as described above, it is important to change the bias at proper timing. The timing is adjusted at any time during correction, based on sensing results of sensors that sense the rotation periods of the development roller and the photoreceptor drum.
In the image forming apparatus, setting to make a linear velocity difference between the image carrier and an intermediate transfer body is employed for purpose of prevention of an abnormal image such as a vermicular image. In the above-described image forming apparatus, although the imaging condition is changed periodically in order to correct the uneven density, the uneven density with the relevant period may be deteriorated. In a four-drum tandem-type image forming apparatus, even if an uneven density level before the correction is the same among colors, the uneven density level may deteriorate in some of the colors, and may improve in the other colors.